windows ethernet networking broken with wintun

[martini2]

Hello,
i have a windows 10 network with 5 computers with a usual network speed of 113MB/s. Two computers have openvpn installed to connect to another network. This setup worked for years until the recent change from tap to wintun.
Now with the vpn service running on both computers the local network speed between the them is 0-100Kb/s. It takes for ever to start copying/moving a file. Aplications start are very slow and are barely usable. The network speed between one of the computers with vpn and another one without vpn is normal. If i stop the vpn service on one of the computers the network speed between them is normal again.
As autometric does not work i have set the metric on both computers to a lower value to prioritize the ethernet, but it has no effect. Reseting the network and reinstalling openvpn or setting the vpn ip to a static value does not help either.
How do i fix this without going back to tap? What info shoud i provide?

[TinCanTech]

Please see: viewtopic.php?f=30&t=22603